Certain applications require use of a thermal transfer printer (TTP), which is a printer that prints on paper, or some other substrate or material, by melting a dried coating of pre-applied ink on a carrier ribbon such that the coating adheres to the substrate being printed upon. TTPs often use electronic print heads with microscopic heating elements which allow for the heating of discrete portions of the ribbon as the ribbon is moved across the print heads, melting only the coating where heat is applied on the discrete portions of the ribbon, and then transferring that coating onto the substrate. Fresh ribbon is typically wrapped around a first cylindrical core of a supply reel, and then is transferred to and wound around a second cylindrical core of a wind-up reel using a series of spindles, guides, and motors.
In one known TTP, the supply reel is mounted onto a supply spindle, the ribbon is threaded through a series of guides and a tensioner, leading to a wind-up reel which is mounted onto a wind-up spindle. The wind-up spindle is connected to a motor, through a belt and a meter roller, and the spent ribbon is wound up around the wind-up reel.
Once the coating is transferred from ribbon onto the substrate, the ribbon is considered spent and as a result, is wound up around the wind-up reel. The wind-up reel may be driven by the metering roller which may be connected with the wind-up spindle via a rubber band, or polyurethane belt, that goes around both the wind-up spindle and the metering roller in a slip drive configuration. Preferably, the gearing between the metering roller and the wind-up spindle is such that one revolution of the metering roller causes more than one revolution of the wind-up reel.
In one know arrangement, the ribbon is wrapped around the metering roller and then onto the wind-up reel. In this configuration, the wind-up reel has a paper-based cylindrical core have an inner diameter DI of approximately 25 mm, ±5 mm. The wall of the cylindrical core is approximately 3 mm, ±2 mm, thick. With reference to FIG. 1, in a traditional wind-up spindle 200, there is often found a friction fitting 202, such as a compression spring, on the wind-up spindle 200 which applies a certain amount of force onto the cylindrical core in order to secure the cylindrical core on the wind-up spindle 200.
Often times the cylindrical cores are not new, and they may be sitting around for some time, gathering humidity, possibly causing their structure to weaken. New supply reels may have as much as 600 meters to 1000 meters of ribbon on them. The ribbon is roughly 30 microns thick, ±10 microns, and is often polyester based, with a heat transferrable coating applied onto the ribbon.
As the ribbon is wound up around the wind-up reel, and specifically the cylindrical core of the wind-up reel, the ribbon tends to wrap itself tighter and tighter around the paper-based cylindrical core. As the diameter of ribbon around the cylindrical core of the wind-up reel grows in size, the tension along the ribbon and around the cylindrical core of the wind-up reel is always changing, and often increasing.
The increasing tension around the around the cylindrical core of the wind-up reel produces an inwardly radial force towards the center of the cylindrical core of the wind-up reel. As a result, many times the tension around the cylindrical core of the wind-up reel is so high that the paper-based cylindrical core of the wind-up reel collapses into itself and around the wind-up spindle, since the cylindrical core of the wind-up reel cannot withstand the high tensions and forces around it. Once the paper-based cylindrical core of the wind-up reel collapses into itself and fuses itself around the wind-up spindle, it becomes very difficult for an operator to remove the collapsed cylindrical core of the wind-up reel from the wind-up spindle. As a result, an operator may have to damage the TTP in order to remove the collapsed cylindrical core from the wind-up spindle, and possibly cause injury to the operator himself/herself in the process. Additionally, removing a collapsed cylindrical core from a wind-up spindle may also cause a significant amount of downtime for the TTP, leading to a loss of manufacturing efficiency.
It would therefore be desirable to have a device and/or method for preventing a cylindrical core of a wind-up reel from collapses into itself and fuses itself around the wind-up spindle.